Urticaria, the medical term for hives, occurs as temporary, small to large, pink, raised lesions on the skin called wheals. These plaques may be associated with itching or even burning, and they may occur in areas of pressure, such as the waistline of trousers.   A systemic reaction of hives is angioedema.  Angioedema leads not only to swelling of the skin, but also of the mucous membranes (around eyes or mouth), gastrointestinal problems, and breathing difficulties.  Severe cases of angioedema can be a symptom of  anaphylaxis - a life-threatening allergic reaction associated with low blood pressure.   Approximately one-half of all cases of hives have no identifiable cause. Recognized causes of urticaria include medications, food allergies, recent viral illness, emotional stress, and even alcohol.  Common medication causes of hives include antibiotics such as penicillin, aspirin, pain medications, and anti-inflammatories (NSAIDs).  Other triggers for urticaria include cold, heat, exercise, water, sun, and excessive vibration.   Most hives are “acute,” meaning they resolve within six weeks of first outbreak. Cases lasting longer than six weeks are referred to as “chronic urticaria.”  Diagnosis in some cases is determined by a skin biopsy.  This is particularly helpful in cases when hives is associated with vasculitis (inflammation of the blood vessels).   The mainstay of hives treatment is oral antihistamines.  Short bursts of oral steroids are used occasionally to bring severe cases of urticaria under control.  For systemic reactions including anaphylaxis, a metered dose of epinephrine may be necessary to carry with the affected person at all times.